The present invention relates to bourdon tube gages and, in particular, to means for exercising the coiled tubes of these gages. The tube portion of the bourdon tube usually is elliptical or flattened in cross-section and bent into a circular or somewhat coiled form. The fluid pressure to be measured is applied to the tube interior through one of its ends while the other end is sealed. A pointer and scale provide direct pressure readings. Usually, the sealed end of the tube is coupled by a link to a pivoted quadrant that is provided with teeth meshed with those of a pinion that is mounted on the pointer spindle. An increase of pressure within the tube tends to change its cross section from elliptical to circular and the tube consequently uncoils slightly to turn the pointer.
Prior to any use, it is desirable to calibrate the gages by admitting known amounts of hydraulic or pneumatic fluid to the tube interior to determine the response of the pointer. However, prior to calibration, it is equally important to conduct a so-called tube-exercising procedure in which the tube is deflected a sufficient amount to produce full scale movements of its pointer and usually each exercising operation repeats the full scale movements several times. For example, U. S. Naval activities customarily require such exercising operations prior to each calibration. The exercising operations are set forth in certain instrument calibration procedures identified as procedures 17-20 mp-01, 17-20 mp-13 and 17-mp-15.
As far as in known, exercising has been accomplished by admitting fluid pressure into the tube interior, and although such procedures have been entirely effective, they are inefficient and uneconomical. For one reason, they are unnecessarily wasteful of the gas used to produce the full scale deflections. In addition, they have proven to be unnecessarily time-consuming. For example, certain gages require the use of high-grade, dry nitrogen gasses both in the exercising and calibration procedures. Such gases are used to maintain an `oxygen clean` condition. Each calibration and exercising procedure requires about 1/3 of a tank of the gas at a material cost per unit of over $18.00. Since the exercising operation alone requires the tube to be filled and pressured full scale at least three times, the major portion of this material expense occurs during the exercising. Further, the gas used in the exercising is bled-off and discarded so that it is entirely wasted. Other gages use a less expensive dry nitrogen but again, the expense of the gas becomes a total loss. Additionally, the man hours needed for exercising a tube by repeatedly admitting gas to the tube interior becomes a factor which can be significantly reduced if the need to admit the gas is eliminated.
Accordingly, it is a primary object of the present invention to provide a means for mechanically exercising bourdon tube gages which is equally as effective and reliable, as well as considerably less expensive, than past exercising methods.
Another object is to provide a pivotal lever arm for physically engaging and mechanically exercising the tube, the apparatus itself being simple, inexpensive and easily and quickly mounted in operative position.